A novel optimization strategy for line loss reduction in distribution networks with large penetration of distributed generation

•Establishing a realistic unbalanced harmonic power flow calculation model.•Establishing DG line loss optimization model with harmonic constraint.•Analyzing several DG line loss optimization schemes in distribution network with multi-type harmonic loads.•The harmonic contents have been decreased but also increased the line loss.•Under the same line loss, the optimal capacity of double DG is less than that of single DG,•The optimization of double DG is better without considering the cost.